by
Bittinger, Marvin L.; Ellenbogen, David J.; Johnson, Barbara L.

Answer

$x^2+7x+12$

Work Step by Step

Using $(a+b)(c+d)=ac+ad+bc+bd$ or the product of $2$ binomials, the given expression, $
(x+3)(x+4)
$, is equivalent to
\begin{array}{l}\require{cancel}
x(x)+x(4)+3(x)+3(4)
\\\\=
x^2+4x+3x+12
\\\\=
x^2+7x+12
.\end{array}